Fluorescent lamps have been frequently used as indoor and outdoor illumination devices. However, they are not lightened in an emergency such as a power supply shutdown. Accordingly, the Building Standards Act of Japan requires that there should be installed emergency lights in commercial facilities and accommodations for the purpose of providing a sufficient degree of illumination to an escape route for evacuation.
However, the conventional emergency lights have been installed individually from the normal illumination devices, which should in practice limit the number and place of the emergency lights to be installed. This means that, in an emergency, only a small number of the emergency lights are lightened in darkness at limited places. Let us imagine that a power supply is accidentally interrupted due to an earthquake or fire in an underground railway or an underground shopping area, for example. The nearby people would tend to be moved to a better-lighted place, which will be strengthened by mass psychology. Therefore, all of the nearby people would rush toward the place of installment of the emergency lights, which could result in an expected accident.
In recent years, LED illumination devices usable in substitution of the existing fluorescent lamps have been proposed (for example, the following Patent Documents 1 and 2). This has well-improved properties such as energy-saving due to its lowered power consumption, ecology due to a decrease of CO2, and safety because of no contents of toxic substance such as mercury and, therefore, it is expected that the LED illumination devices will come into wider use in future. Nevertheless, it has been less contemplated that the LED illumination devices should be used in an emergency such as a power supply shutdown                Patent Document 1: Japanese Patent (Un-examined) Publication No. 2004-192833        Patent Document 2: Japanese Patent (Un-examined) Publication No. 2004-303614        